Headspace sampling devices and systems typically include a vial configured to receive and hold a sample and to receive a sparging or inert gas. The gas carries headspace vapor from the vial to an analytical device. The vial may include a diaphragm or septum to seal the vial such that a probe can be inserted in the septum to provide a flow of the sparging gas from the sample headspace in the vial for transmission of the gas to an analytical instrument, which analyzes the headspace gas.
Sampling methods from headspaces may be either static or dynamic. In static methods, one typically pressurizes a sealed vial or vessel containing the condensed analyte (to slightly above atmospheric pressure), then sampling may be done of the pressurized headspace through a septum. Sampling may be done with a gas tight syringe (with or without a syringe valve), a multiport sampling valve, or with a solid phase micro extraction (SPME) fiber. In dynamic methods, a flow of carrier or sweep gas may be applied to the matrix containing the analyte. The stream may then be collected in a cryostat, adsorbent or solvent, thus this method is often referred to as purge and trap. The sweep gas may be under a positive pressure or drawn through the sample at reduced pressure.
When the analyte in the headspace gas is at a trace level, or when an exhaustive analysis of all constituents is desired, purge and trap methods are often preferred over static headspace or even modern SPME approaches. For analytes of very low volatility, longer collection times are required to collect sufficient sample for analysis. One means of obtaining a sample and introducing it into an analytical instrument, such as a chromatographic column, is known as headspace sampling. In conventional headspace sampling, sample material is sealed in a vial and subjected to constant temperature conditions for a specified time. Analyte concentrations in the vial gas phase should reach equilibrium with the liquid and/or solid phases during this thermostatting time. The vial is subsequently pressurized with carrier gas to a level greater than the “natural” internal pressure resulting from thermostatting and equilibration. Then the pressurized vial is connected to the chromatographic column in such a way as to allow for the transfer of a portion of the vial gas phase into the column for a short period of time.
Gas chromatography is an analytical instrument used for the separation of compounds for the purpose of purification, identification, and quantification. The sparging gas having the sample entrained therein can be injected into a gas chromatograph for compositional analysis and to provide an output that indicates a substance in the sample.
The art is receptive to articles and processes that provide for sampling an analyte.